In the field of nuclear medicine, positron emission tomography (PET) devices have been the focus of attention. A target substance having positron emission capability is introduced into a subject. The target substance emits γ-rays due to electron-positron pair annihilation. PET devices measure the spatial distribution of the concentration of the γ-rays emitted from the target substance at a specific area. The PET device then performs imaging process based on the spatial distribution of the concentration of the γ-rays and, from the image processing, detects accumulations of the target substance in the specific area.
For example, fluorodeoxyglucose (FDG) is injected into the body of a patient and, PET devices detect a developing malignant tumor by measuring spatial distribution of the concentration of the γ-rays emitted from the FDG and perform image processing based on the measured spatial distribution of the concentration of the γ-rays. The FDG is created by binding a radio-isotope to pseudo glucose. Glucose metabolism is about three times to eight times higher in a malignant tumor, such as cancer, than a normal cell. Therefore, there is a higher concentration of the pseudo glucose at malignant tumors. Because FDG, which is injected into the subject, contains pseudo glucose, the concentration of γ-rays, which are generated due to the presence of the FDG, changes at the location of a malignant tumor. As a result, it becomes possible to detect malignant tumors with PET devices. PET devices are sensitive enough to detect a slight lesion even if the lesion cannot be found by computerized tomography (CT) devices. This is greatly contributing to the early detection of cancers.
However, the spatial resolution of PET devices is inferior to that of CT devices because of their configuration. In other words, PET devices can detect slight lesions but cannot identify the precise location of the lesions. As a countermeasure, instead of using just PET devices to capture in-vivo images, so-called PET-CT devices have already been put into practice in which a PET device and a CT device are combined to capture images of the same subject. In other words, a PET device is used to detect whether a lesion is present, and a CT device is used to capture images of an in vivo structure within the subject. The images are then superimposed to identify the location of the lesion, which has been detected by the PET device. Although CT devices are inferior to PET devices in detecting the presence of the lesion, the CT devices have excellent spatial resolution. Therefore, PET-CT devices are advantageous in that they can detect a slight lesion with high precision and identify the exact location of the lesion (see Japanese Patent KOHYO Publication No. 2003-501666).